Makai de Sodaterareta Shounen, Umarete Hajimete no Ningenkai de Musousuru: Makai no Joushiki de Ikitetara, Kizukeba Jinrui Saikyou ni Natteita (Light Novel)

Soon after Eder was born, he fell into the demon world, where fiendish demons strut around. His life was thankfully saved by the Great Sage Ramírez, but after a constant change of landscape, he descends upon a forest where Bahamut finds him and, treating him as though he's a small-fry monster, gives him a very non-standard upbringing in the demon world! When Eder turns 12, Ramírez passes away, so the boy heads for the human world and enrolls in a school for heroes. During his life on campus, he tries to inconspiculously breeze through his lessons in dungeon exploration and magic, but those around him notice him right away. He asks them, "Isn't what I'm doing normal?" But because Eder shows off his extraordinary powers, they all dig into him and say, "It's weird to think that THIS is normal!" Because Eder was raised in such an absurdly hard environment, can he survive in the human world where his common sense doesn't apply?!